1. Field of the Invention:
This invention relates to an information signal recording apparatus and more particularly to an information signal recording apparatus having a rotary or flying erase head (hereinafter referred to as FEH for short).
2. Description of the Related Art:
Heretofore, it has been practiced that, when an information signal such as a video signal or the like is recorded by a rotary head, a control signal (hereinafter referred to as CTL signal) is recorded by a control head (hereinafter referred to as CTL head) by forming a recording track on a tape-shaped recording medium in the longitudinal direction of the medium in addition to helical recording tracks formed by the rotary head. This is called the CTL method. The conventional rotary head type information signal recording and reproducing apparatus operating by the CTL method is arranged to determine timing for the start of recording by using a reproduced CTL signal in carrying out the so-called concatenated recording, i.e. recording continuously from a part already recorded. Meanwhile, a recording and reproducing apparatus of another kind performing tracking control by the so-called four-frequency method must be arranged differently from the apparatus performing tracking control by the CTL method. The tracking control by the above-stated four-frequency method is as briefly described below:
FIG. 1 of the accompanying drawings shows a pattern of magnetized recording tracks formed by a video tape recorder (hereinafter referred to as VTR) of the kind performing tracking control by the four-frequency method. FIG. 2 is a block diagram showing the essential parts of a tracking error signal processing circuit employed in the conventional VTR. Referring to FIG. 1, a magnetic tape 1 is arranged to be moved in the direction of arrow 2. Recording tracks A1, B1, A2, B2, ---are formed with signals recorded by heads A and B which have azimuth angles different from each other. An arrow 3 indicates the scanning direction of the heads. In recording tracks 4 are recorded along with a video signal pilot signals of four different frequencies f1 to f4. One of the pilot signals is recorded for every field, or one in each of the tracks in rotation. The sequence in which the pilot signals are recorded is as shown in FIG. 1. For example, the pilot signal of frequency f1 which is 102.5 KHz.apprxeq.6.5 fH is recorded in the recording track A1; the pilot signal of frequency f2 which is 118.9 KHz.apprxeq.7.5 fH is recorded in the track B1; the pilot signal of frequency f3 which is 165.2 KHz.apprxeq.10.5 fH in the track A2; and the pilot signal of frequency f4 which is 148.7 KHz.apprxeq.9.5 fH in the track B2 (fH being the frequency of a horizontal synchronizing signal). These pilot signals are recorded in a state of being superimposed on a video signal. The frequency difference between the pilot signals recorded in adjacent recording tracks is either fH or 3 fH as shown in FIG. 1. When the head is scanning the tracks Ai (i: 1, 2, 3, ---), the frequency difference is always fH between the pilot signal of the track being mainly scanned and that of the adjoining track on the right-hand side and always 3 fH between the pilot signal of the track and that of the adjoining track on the left-hand side. Further, when the head is scanning the tracks Bi (i: 1, 2, 3, ---), the frequency difference is always 3 fH between the pilot signal of the track being scanned and that of the adjoining track on the right-hand side and always fH between the pilot signal of the track being scanned and that of the adjoining track on the left-hand side.
Since the frequencies f1 to f4 of the pilot signals are relatively low, the pilot signals recorded in the adjacent tracks other than the track being mainly scanned can be reproduced by the head as cross-talks even in the event of azimuth recording. Assuming that the head is mainly scanning the track A2, the pilot signal thus detected is a composite signal including components of frequencies f4, f2 and f3. In case that the center of the tracing locus of the head precisely coincides with the center line of the track which is mainly scanned under the tracking control, i.e. in the case of on-track, the pilot signals (of frequencies) f2 and f4 of the neighboring tracks are reproduced at even levels. However, the level of the frequency component f4 becomes higher than that of the other frequency component f2 when the position of the head slightly deviates from the center line of the track A2 toward the track B2 and lower than that of the component f2 when the position of the head deviates toward the track B1.
Therefore, with difference signals which represent the frequency differences fH and 3 fH between the pilot signal recorded in the mainly scanning track and the pilot signals recorded in the two neighboring tracks separately taken out, the deviating direction and the deviating degree of the head from the main scanning track are obtainable by comparing the levels of these two difference signals.
FIG. 2 shows in a block diagram the circuit arrangement of the VTR operating by the four-frequency method described above. Referring to FIG. 2, a reproduced signal consisting of a video signal and the pilot signals which are superimposed on each other comes from a terminal 5 to a low-pass filter (LPF) 6. The LPF 6 then separates the pilot signal component from the incoming reproduced signal. A multiplier 8 is arranged to perform a multiplying operation on the pilot signal component and a local pilot signal which is generated by a local pilot signal generating circuit 7. The circuit 7 is arranged to produce a pilot signal of the same frequency as that of the pilot signal recorded in the mainly scanning track. Then, since as mentioned above with reference to FIG. 1, the output of the LPF includes the frequency components f2, f4 and f3 with the track A2 assumed to be mainly scanned, the local pilot signal has the frequency f3 in this instance. Therefore, the multiplier 8 produces a signal having frequencies representing the sum of and a difference between the frequency f3 and the frequency components f2, f4 and f3. A band-pass filter (BPF) 9 is arranged to take out only a signal of frequency fH from the sum and difference signal while another BPF 10 is arranged to take out a signal of frequency 3 fH. The outputs of these BPFs are supplied to detection circuits 11 and 12 for detection and rectification.
The signal components fH and 3 fH which are thus obtained from the circuits 11 and 12 are then supplied to a level comparison circuit 13. The circuit 13 then produces a signal representing a level difference thus obtained. More specifically, when the reproduced level of the signal fH is higher than that of the signal 3 fH, a positive potential corresponding to the level difference is obtained. A negative potential is obtained in the opposite case. By this a signal including information on the track deviating degree and track deviating direction of the head is produced and can be used as a tracking error signal.
Under this condition, the relation between the deviating direction and the tracking error signal obtained for the track A1 becomes reverse to the relation obtained for another track B1 as mentioned in the foregoing with reference to FIG. 1. To solve this problem, a switching circuit 16 is arranged behind the level comparison circuit 13 to have the output of the comparison circuit 13 selectively produced either through an inverting amplifier 14 or not through the amplifier 14 in accordance with a head switch-over signal 15.
Some of the VTR employing the above-stated four-frequency method, such as the known 8 mm VTR, is arranged to have different tape moving speed modes for recording and reproduction including a mode in which tape is allowed to travel at a standard speed (hereinafter referred to as the SP mode), a mode in which the tape is allowed to travel at a speed 1/2 of the SP mode (hereinafter referred to as the LP mode) and another mode in which the tape is allowed at a speed 1/3 of the SP mode (hereinafter referred to as the EP mode) for example. In performing the so-called concatenated recording with such a VTR, it is difficult to appositely determine timing for the start of recording when the tape speed is switched from one speed to another. In other words, in carrying out cancatenated recording in the manner generally practiced, the tape is rewound to an extent corresponding to a given number of tracks and, after that, recording is allowed to begin at a point of time at which the tape has been allowed to travel to the extent corresponding to the given number of tracks. In that instance, an existing record tends to be left unrecorded. Thus, it has been difficult to make the recorded pattern of an information signal adequately continuous.